A number of watches and clocks have been devised which are entirely electronic in operation, using no moving mechanical parts in the timekeeping or time display functions. A recent one of these uses an oscillating quartz crystal as a frequency standard; counting and decoding circuits convert the crystal output to a form and frequency suitable to operate a display. A typical realization using a liquid crystal display is illustrated in U.S. Pat. No. 3,505,804 by S. R. Hofstein. A commercially available wristwatch uses a display of light emitting diodes. Several all solid-state wristwatches with liquid crystal displays have been announced for retail introduction in the near future.
While the electronic "movements" of these watches are potentially simpler and cheaper than conventional mechanical watches of equivalent accuracy, the outer cases which are used are both more costly and complex. One reason is that electrical switches must be provided to allow setting of the timepiece. These switches are considerably smaller than commercially available switches and their size presents difficulties of manufacture. In addition, they must not compromise the water-tight integrity of the case, must lend themselves to attractive styling, and maintain reliability in all the environmental circumstances to which watches are subjected. Consequently, watch cases embodying such switches, are and will continue to be more expensive than conventional watch cases. In addition, labor costs are incurred in assembling such watches, since appropriate connections must be made to each switch. This extra manufacturing operation does not readily lend itself to automated production.
An alternative to conventional mechanical switches may be to use some internal switches activated by non-mechanical means. For example, one commercially available watch uses sealed "reed switches" within the case, actuated by proximity to a small magnet provided with the bracelet. While this is possible, it requires relatively costly and fragile switches, and a unique activating device. A second alternative described in U.S. Pat. No. 3,485,033 to L. W. Langley is to employ a light responsive element located within the watch which may be activated by shining a bright beam of light onto that element. This too appears to be a fairly costly and somewhat inconvenient technique.